1. Observational Frontiers in the Multiplicity of Young Stars
Karl E. Haisch Jr. (UVSC), Mary Barsony (SFSU)
Gaspard Duchêne (Grenoble Obs.)
Eduardo Delgado-Donate (Stockholm Obs.)
Thomas P. Greene (NASA ARC), Laurent Loinard (UNAM)
Luis F. Rodríguez (UNAM), Steve Stahler (UC Berkeley)

2. Presentation Outline Why study young multiple systems?
T Tauri multiple systems
Embedded multiple systems
Summary
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

3. Importance of Multiple Systems
Multiple stellar systems are ubiquitous
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

4. Importance of Multiple Systems
Multiple stellar systems are ubiquitous
They result from core fragmentation and later interact with stars and gas
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

5. Importance of Multiple Systems
Multiple stellar systems are ubiquitous
They result from core fragmentation and later interact with stars and gas
Their statistical properties depend on the physical processes at play
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

6. Importance of Multiple Systems
Multiple stellar systems are ubiquitous
They result from core fragmentation and later interact with stars and gas
Their statistical properties depend on the physical processes at play
Multiple systems are a probe of the star formation process
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

7. Early Multiplicity Surveys
Surveys of young stellar populations were conducted in the 1990s
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

8. Early Multiplicity Surveys
Surveys of young stellar populations were conducted in the 1990s
Very high multiplicity in all of them, in some cases even higher than field stars
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

9. Early Multiplicity Surveys
Surveys of young stellar populations were conducted in the 1990s
Very high multiplicity in all of them, in some cases even higher than field stars
Environment-dependent behavior (clusters vs. “T associations”)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

10. Early Multiplicity Surveys
Surveys of young stellar populations were conducted in the 1990s
Very high multiplicity in all of them, in some cases even higher than field stars
Environment-dependent behavior (clusters vs. “T associations”)
Initial conditions or evolutionary effect?
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

11. Early Multiplicity Surveys
Surveys of young stellar populations were conducted in the 1990s
Very high multiplicity in all of them, in some cases even higher than field stars
Environment-dependent behavior (clusters vs. “T associations”)
Initial conditions or evolutionary effect?
Tremendous observational progress in this field
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

12. Low-Mass T Tauri Multiples
Early surveys primarily focused on M T Tauri stars
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

13. Low-Mass T Tauri Multiples
Early surveys primarily focused on M T Tauri stars
Sampling M<0.5 M objects
is critical to constrain models
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

14. Low-Mass T Tauri Multiples
Early surveys primarily focused on M T Tauri stars
Sampling M<0.5 M objects
is critical to constrain models
Low-mass stellar multiples
in the Taurus cloud are
much tighter (sep. < 60 AU)
more equal mass (q > 0.7)
slightly less frequent
proj
MB / MA
Multiplicity
White et al. (2006)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

15. High-Order T Tauri Multiples
Among field stars, there are ~4 binaries for each triple/quadruple/… system
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

16. High-Order T Tauri Multiples
Among field stars, there are ~4 binaries for each triple/quadruple/… system
Targeting known binary T Tauri stars reveals at least as many triple systems
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

17. High-Order T Tauri Multiples
Among field stars, there are ~4 binaries for each triple/quadruple/… system
Targeting known binary T Tauri stars reveals at least as many triple systems
Even if considering only visual companions
Also true for tight spectroscopic binaries
Koresko (2000), Melo (2003), Correia et al. (2006)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

18. High-Order T Tauri Multiples
Among field stars, there are ~4 binaries for each triple/quadruple/… system
Targeting known binary T Tauri stars reveals at least as many triple systems
Even if considering only visual companions
Also true for tight spectroscopic binaries
Possible overabundance to be confirmed
Koresko (2000), Melo (2003), Correia et al. (2006)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

19. Probing Even Younger Systems
Core fragmentation occurs in ≤ 1 Myr, after that only star-star dynamics play
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

20. Probing Even Younger Systems
Core fragmentation occurs in ≤ 1 Myr, after that only star-star dynamics play
For an isolated core, the whole evolution is over by the T Tauri phase
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

21. Probing Even Younger Systems
Core fragmentation occurs in ≤ 1 Myr, after that only star-star dynamics play
For an isolated core, the whole evolution is over by the T Tauri phase
Need to search for youngest multiples
to constrain fragmentation “as it occurs”
to better test influence of environment
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

22. Probing Even Younger Systems
Core fragmentation occurs in ≤ 1 Myr, after that only star-star dynamics play
For an isolated core, the whole evolution is over by the T Tauri phase
Need to search for youngest multiples
to constrain fragmentation “as it occurs”
to better test influence of environment
Multiplicity surveys of Class 0/I sources
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

23. Multiplicity of Embedded YSOs
First surveys conducted in radio domain
Looney et al. (2000), Reipurth et al. (2002, 2004)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

24. Multiplicity of Embedded YSOs
First surveys conducted in radio domain
Looney et al. (2000), Reipurth et al. (2002, 2004)
Larger surveys later conducted in NIR
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

25. Multiplicity of Embedded YSOs
First surveys conducted in radio domain
Looney et al. (2000), Reipurth et al. (2002, 2004)
Larger surveys later conducted in NIR
Similar findings: high multiplicity, similar to T Tauri stars’ excess AU
field
Tau
Oph
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

26. Multiplicity of Embedded YSOs
First surveys conducted in radio domain
Looney et al. (2000), Reipurth et al. (2002, 2004)
Larger surveys later conducted in NIR
Similar findings: high multiplicity, similar to T Tauri stars’ excess
No difference between
molecular clouds
Haisch et al. (2002, 2004)
Duchêne et al. (2004, 2006) AU
field
Tau
Oph
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

27. Sample of Nearby Dark Clouds
Cloud Distance (pc) # Objects Refs
Perseus
Taurus-Auriga
 Ophiuchus ,4
Chamaeleon I, II ,6,7
Serpens 93
Ladd et al. (1993)
Kenyon & Hartmann (1995)
Wilking et al. (1989)
Greene et al. (1994)
5. & 6. Prusti et al. (1992a,b)
7. Persi et al. (1999)
8. Kass et al. (1999)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

28. Near-IR Observations JHKL band Imaging Instruments: OSIRIS, NSFCAM
Telescopes: Cerro Tololo Interamerican Observatory 4.0 m.
NASA Infrared Telescope Facility 3.0 m
Plate Scales: arcsec/pix (CTIO)
0.148 arcsec/pix (IRTF)
Sensitivity limits: mK,H,J = 18.5, 19.5, 20.5 (CTIO)
mK,H,J = 19.0, 20.0, 21.0 (IRTF)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

29. Multiple Companion Star Fractions
CSF = B + 2T + 3Q / (S + B + T+Q)
where S = # singles, B = # binaries, T = # triples, Q = # quadruples
Restrictions: Separation = 100 – 2000 AU
Mag difference K = 4
 Class I/flat-spectrum CSF = 18%  4%
 T Tauri Star CSF for same regions = 19%  3%
 CSF for solar-type and M-dwarf main sequence stars = 11%  3%
Similar results have been found in adaptive optics survey of 44
Class I YSOs by Duchene et al. (2006), which covers a
separation range of AU.
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

30. Multiplicity of Embedded YSOs
Core fragmentation independent on large physical scales; only sensitive to small-scale physics which may be very similar in all molecular clouds
No dense association of  5 protostars
- If cores fragment into that many independent seeds, they
must decay into unbound stable configurations within a very
short timescale, on order 105 years
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

31. Mid-IR Protostellar Binary Survey
Surveyed 64 sources from near-IR survey at N-band (10.3 m)
using Univ. of Arizona m imager MIRAC3/BLINC at the
Magellan 6.5 m telescope on Las Campanas, Chile, and JPL
µm imager MIRLIN at Palomar Observatory in California.
- MIRAC Plate scale = arcsec/pix  field of view 15.7’’ x 15.7’’
- MIRLIN Plate scale = arcsec/pix  field of view 19.2’’ x 19.2’’
Detected 45/48 (94%) of the single sources, 16/16 (100%) of
the primary components, and 12/16 (75%) of the
secondary/triple components of the binary/multiple objects
surveyed.
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

32. Young Stellar Object Spectral Energy Distributions
Class I ( > 0.3)
Flat Spectrum (0.3 >   -0.3),
Class II (-0.3 >   -1.6)
Class III ( < -1.6)
Spectral Index
 = dlog(F)/dlog()
e.g. Adams, Lada & Shu (1987)
Adams, Shu & Lada. (1988)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

33. JHKL Color-Color Diagram for Multiples
Haisch et al. (2006)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

34. KLN Color-Color Diagram for Multiples
Haisch et al. (2006)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

35. Multiple protostar evolutionary status
Color-color diagrams generally indicate clear progression from Class I  FS  Class II
Extinction estimates, AV, similar for individual
binary/multiple components
ISO-Cha I 97 is a binary star, in which the
secondary has very steep spectral index
  3.9; member of very rare YSO class
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

36. Interesting Case: ISO-Cha I 97
Sep’n = 2.95 arcsec; PA = 72.6 deg. N
Secondary has spectral index  ≥ 3.9!
Haisch et al. (2004, 2006)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

37.  Ophiuchi Binary WL 1 Haisch et al. (2002)
 = -0.5 N
 = -0.7 E
Both Class II
Sep’n = 0.82 arcsec; PA = 321 deg.
Haisch et al. (2002)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

38.  Ophiuchi binary L1689 IRS 5 Haisch et al. (2002, 2004)
N is flat-spectrum
S is Class II
Sep’n = 2.92 arcsec; PA = 240 deg.
Haisch et al. (2002, 2004)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

39. Comparison of Primary/Secondary Spectral Indices for Class I YSOs
Haisch et al. (2006)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

40. Comparison of Primary/Secondary Spectral Indices for Class II YSOs
Haisch et al. (2006)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

41. Implications There appears to be a higher proportion of mixed
Class I/Flat-Spectrum systems (65-80%) than
that found in mixed Class II systems (25-40%)
Given the low likelihood of misclassification of
Class I and Class II YSOs, this demonstrates
that the envelopes of Class I/Flat-Spectrum
systems are rapidly evolving during this phase
of evolution, although they still may be coeval.
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

42. Some Peculiar Embedded YSOs
Surveys revealed “mixed” systems with embedded and non-embedded objects
non-coeval objects in bound systems?
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

43. Some Peculiar Embedded YSOs
Surveys revealed “mixed” systems with embedded and non-embedded objects
non-coeval objects in bound systems?
What do they tell us exactly?
Inadequate Class 0-I-II-III sequence
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

44. Some Peculiar Embedded YSOs
Surveys revealed “mixed” systems with embedded and non-embedded objects
non-coeval objects in bound systems?
What do they tell us exactly?
Inadequate Class 0-I-II-III sequence
Abrupt evolutionary changes (disruptions?)
Misclassification due to peculiar geometry
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

45. Some Peculiar Embedded YSOs
Surveys revealed “mixed” systems with embedded and non-embedded objects
non-coeval objects in bound systems?
What do they tell us exactly?
Inadequate Class 0-I-II-III sequence
Abrupt evolutionary changes (disruptions?)
Misclassification due to peculiar geometry
Dedicated follow-up studies needed
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

46. The Earliest Dynamical Masses
Orbital motion of embedded binaries is achievable with VL(B)A observations
Mdyn (M)
proj (AU)
Porb (yr)
IRAS 40
YLW 15 70
360
IRAS 25
L 1551 IRS 5 45
260
Loinard (2002), Loinard et al. (2002)
Curiel et al. (2003), Rodríguez et al. (2003)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

47. The Earliest Dynamical Masses
Orbital motion of embedded binaries is achievable with VL(B)A observations
Mdyn (M)
proj (AU)
Porb (yr)
IRAS
2.8 ± 0.7 40
YLW 15
1.7 ± 0.8 70
360
IRAS
1.0 ± 0.5 25
L 1551 IRS 5
1.2 ± 0.5 45
260
Comparable mass to T Tauri systems
Loinard (2002), Loinard et al. (2002)
Curiel et al. (2003), Rodríguez et al. (2003)
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

48. Conclusions No dense associations of 5 or more protostars found on
Protostellar companion star fraction x T Tauri and
Main Sequence fraction.
No evidence that any star-forming region presents a
significantly higher/lower multiplicity rate.
No significant evolution of the multiple system population
found within the ≤ 1 Myr timescale during which protostars
evolve into optically bright T Tauri stars.
No dense associations of 5 or more protostars found on
spatial scales ≤ 2000 AU.
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007

49. Conclusions (cont.)
Extinction estimates, AV, are generally similar for individual
binary/multiple components.
Many of the individual component SEDs display mixed
pairings which is not consistent with what one typically
finds for T Tauri stars.
ISO-Cha I 97 is a binary star, in which the secondary has
a very steep spectral index of a ≥ 3.9. Member of a rare
class of YSO i.e., those with a > 3. Only 3 such objects
previously known.
Observational Frontiers In The Multiplicity Of Young Stars
From Stars to Planets - April 12, 2007